Ever increasing fuel costs have emphasized the need for minimizing heat loss in structures such as dwellings, industrial buildings and offices. Although heat loss has been reduced through the installation of fixed insulation in walls, ceilings and the like without adversely affecting the functionality of the building, a major source of heat loss in buildings comprised windows which presented significant problems in conjunction with heat loss. Some insulation measures heretofore proposed included the permanent or semipermanent sealing of windows during seasons of adverse weather conditions which precluded easy operability for ventilation purposes. Other insulation approaches further encompassed blocking such windows with insulation materials thereby precluding their use for illumination, observation and as a portal for solar radiant heat.
The prior employment of double and/or triple glazing over existing lights was accomplished only with costly installation and equipment expenditures and did not preclude energy losses through the window casings.
One approach toward low cost window insulation was illustrated in Movable Insulation by William K. Langdon. Such approach involved the use of pop-in shutters comprising insulating panels secured to the window casing. Langdon described a friction fit pop-in shutter which required a wooden peripheral edge framing glued to a foam board to prevent binding of the board. Unfortunately, the construction technique mandated precise measurement of the window casing and low tolerances in cutting an insulation board to size. For example, 3 mm. (1/8 inch) was allotted for compression of a 5 mm. (3/16 inch) peripheral gasket. An undercut of 3 mm. (1/8 inch) prevented a peripheral seal from forming around a panel. Board cutting became even more difficult when the window casings were not square.
Due to the low tolerances required for constructing such shutters, average do-it-yourself homeowners encountered significant difficulties. Tolerance levels were not within the ambit of these individuals, insulation board material was wasted, and attempts at construction resulted in frustration. Further, because of the tight fit, handles or clips were necessary for insertion or removal.